Optical spectroscopy techniques have been developed for a wide variety of uses within the medical community. For example, pulse oximetry and capnography instruments are in widespread use at hospitals, both in the surgery suites and the post-op ICU's. These technologies have historically been based on absorption-based spectroscopy techniques and have typically been used as trend monitors in critical care environments where it is necessary to quickly determine if a patient's vital parameters are undergoing large physiologic changes. Given this operating environment, it has been acceptable for these devices to have somewhat relaxed precision and accuracy requirements, given the clinical need for real-time point-of-care data for patients in critical care situations.
Both pulse oximeters and capnography instruments can be labeled as non-invasive in that neither require penetration of the outer skin or tissue to make a measurement, nor do they require a blood or serum sample from the patient to custom calibrate the instrument to each individual patient. These instruments typically have pre-selected global calibration coefficients that have been determined from clinical trial results over a large patient population, and the results represent statistical averages over such variables as patient age, sex, race, and the like.
There is, however, a growing desire within the medical community for non-invasive instruments for use in such areas as the emergency room, critical care ICU's, and trauma centers where fast and accurate data are needed for patients in potentially life threatening situations. Typically, these patients are not anesthetized and motion-induced artifacts may corrupt data from patient-attached monitoring instruments. Also, patients in shock or acute trauma may have oxygen saturation levels well below the normal physiologic range, or may suffer from reduced blood flow.